[Wien] Fwd: not getting convergence with MBJ potential
Peter Blaha
pblaha at theochem.tuwien.ac.at
Mon Dec 12 16:02:45 CET 2011
If your geometry is not correct, you cannot expect that the bandgaps are correct or
even metal/insulator state comes out correctly.
The experimental lattice parameters are usually ok, even in the simplest experiments, but the positions of
light elements (oxygen) vs. heavier ones are NOT. Thus I would take the exp. lattice parameters, but when
forces are big (<10-20 mRy/bohr), you need to run a couple of min steps.
In all charge-transfer insulators you have the gap between O-2p and TM-d states and you CAN influence the
gap by LDA+U. Larger U simply shifts the upper Hubbard band up and makes a larger gap to O-2p. (PS: I'm
not arguing that LDA+U necessarily describes the physics correctly, but usually it does what one tells it).
PPS: Have you done optics ? Eventually matrix elements may influence the absorption and you cannot just look into the DOS.
> b) We have done UV-visible band gap measurement on this material and it is 3.26 eV. But as you have said properly it is indeed coming as metal after getting converged in 80
> iterations. But we have noticed that there are presence of O p orbital between upper and lower Hubbard band of transition metal atom and hence GGA+U will not improve the situation.
>
> c) At the moment we are a bit handicapped for doing Geometrical (both lattice parameter and atomic coordinates) optimization of 56 atoms unit cell structure as we do not have the
> facility of cluster. Hence as a first approximation we are first trying to reach as near as possible to the accurate electronic structure. We are soon going to get the facility
> and then we can use geometrical optimization.
> And hence we really do have large forces on the structure.
>
> d) We have used a greed of 0.2 and 0.15 both for PRATT mixing and we have not used MSR1 mixing for mbj potential yet.
>
> Sir, as far as the above discussion is concerned we might have our structure wrong (need more accurate TEM analysis!) or Geometrical optimization may solve the problem. But as we
> are now trying to experiment with test run we and as it seems GGA+U can not solve the problem we have opted for mbj potential.
>
> But as you have said if the structure is wrong (we are not yet confirmed though) we may never reach the convergence or desired electronic structure!
>
> Thank you very much for your help Sir.
>
> On Mon, Dec 12, 2011 at 6:52 PM, Laurence Marks <L-marks at northwestern.edu <mailto:L-marks at northwestern.edu>> wrote:
>
> I wonder whether you really have the structure right.
>
> a) When you say that you get the same structure, what R-factor? Powder
> diffraction is not very sensitive to oxygen positions in the presence
> of heavy metal atoms.
>
> b) If GGA takes about 80 iterations I suspect that you have a metal.
> If you do not have the correct number of oxygen versus metal atoms you
> will get this, and no amount of U or mBJ will change this (in 99% of
> cases). Check the bond-valence sums of your model, are the numbers
> reasonable? This is a standard test in solid-state chemistry.
>
> c) Do you have large forces (as Peter asked)? If you do this also
> indicates that you have the structure wrong.
>
> d) When you say that you were using a greed of 0.2 (please do not use
> the term "mixing factor", it is misleading) was this for Pratt or
> MSR1? A change from 0.2 to 0.15 with MSR1 will not matter much.
>
> 2011/12/12 shamik chakrabarti <shamikphy at gmail.com <mailto:shamikphy at gmail.com>>:
> > Dear Dr Peter Blaha and Dr Pascal,
> >
> > The material is a ferrimagnetic transition
> > metal compound and a charge transfer insulator and the gap is between d and
> > O p states. Yes we have started MBJ potential calculation from the converged
> > GGA charge density. So what we can do, we can start from the scratch with
> > MBJ potential and after few iterations will get shifted to MSR1 mixing to
> > improve the convergence. We hope that will help. Thank you for all your
> > helps.
> >
> > with regards,
> >
> >
> > On Mon, Dec 12, 2011 at 1:31 PM, pascal boulet
> > <pascal.boulet at univ-provence.fr <mailto:pascal.boulet at univ-provence.fr>> wrote:
> >>
> >>
> >> Dear Dr. Chakrabarti,
> >>
> >> All right. So, another idea: could it be that you restarted your m-BJ
> >> calculation using the converged GGA or GGA+U density? I ran into these
> >> kinds of troubles several times. I found it preferable to start from
> >> scratch...
> >>
> >> Hope this help,
> >> Pascal
> >>
> >> On 12/12/2011 08:45, shamik chakrabarti wrote:
> >> > Dear Dr. Pascal,
> >> >
> >> > As we were getting Ghost band error due to large
> >> > charge fluctuation during initial cycle *we have reduced the mixing
> >> > parameter from 0.2 to 0.15 & hence thereafter we have not received
> >> > ghost band error yet.*
> >> >
> >> > As long as variation of RMT is concerned the variation is only from
> >> > 1.7 to 2.01 in the structure.
> >> >
> >> > So far there is no energy equivalence between a local orbital and
> >> > overall energy parameter which can induce ghost band error.
> >> >
> >> > Also we have achieved convergence of -0.000034 with plain GGA and only
> >> > with MBJ potential we are getting the convergence problem and again
> >> > plain GGA and also GGA+U have not given the proper electronic structure.
> >> >
> >> > As far as the structure is concerned we are very much sure about its
> >> > structural parameters as they are giving the same XRD as experiment
> >> > when the positional coordinates and lattice parameters of the 56 atom
> >> > cell were put into a software powdcell.
> >> >
> >> > looking forwards to your comments.
> >> >
> >> > with regards,
> >> > On Mon, Dec 12, 2011 at 12:26 PM, pascal boulet
> >> > <pascal.boulet at univ-provence.fr <mailto:pascal.boulet at univ-provence.fr>
> >> > <mailto:pascal.boulet at univ-provence.fr <mailto:pascal.boulet at univ-provence.fr>>> wrote:
> >> >
> >> > Hello,
> >> >
> >> > It is strange that you have such a bad convergence on the energy
> >> > and the
> >> > charge after that many cycles.
> >> > My feeling is that something is wrong in the input.
> >> >
> >> > Have a look at the user manual. From page 205 on, there is an
> >> > explanation of the meaning of ghost bands. You have to experiment on
> >> > your chemical system to get rid of them.
> >> >
> >> > Pascal
> >> >
> >> >
> >> > On 12/12/2011 05:21, shamik chakrabarti wrote:
> >> > > Dear wien2k users,
> >> > >
> >> > > Any response of my previous mail will be
> >> > very
> >> > > helpful for us. Eagerly waiting for your comments.
> >> > >
> >> > > with regards,
> >> > >
> >> > > ---------- Forwarded message ----------
> >> > > From: *shamik chakrabarti* <shamikphy at gmail.com <mailto:shamikphy at gmail.com>
> >> > <mailto:shamikphy at gmail.com <mailto:shamikphy at gmail.com>>
> >> > > <mailto:shamikphy at gmail.com <mailto:shamikphy at gmail.com> <mailto:shamikphy at gmail.com <mailto:shamikphy at gmail.com>>>>
> >> > > Date: Sun, Dec 11, 2011 at 5:42 PM
> >> > > Subject: not getting convergence with MBJ potential
> >> > > To: A Mailing list for WIEN2k users
> >> > <wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>
> >> > <mailto:wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>>
> >> > > <mailto:wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>
> >> > <mailto:wien at zeus.theochem.tuwien.ac.at <mailto:wien at zeus.theochem.tuwien.ac.at>>>>
> >> > >
> >> > >
> >> > > Dear wien2k users,
> >> > >
> >> > > I am trying to simulate electronic
> >> > structure of
> >> > > a charge transfer insulator. Our system consists of a unit cell
> >> > having
> >> > > 56 atoms and we are using 14 k-points. As GGA+U method was failed
> >> > to
> >> > > reproduce the proper band gap (in fact much less than the
> >> > > experimentally obtained one) we have opted for MBJ potential.
> >> > > *Initially the mixing parameter was set to 0.2 and we got Ghost
> >> > band
> >> > > error after few iterations. Hence we reduce the mixing parameter
> >> > to
> >> > > 0.15.* Until now still it has shown no error except some extra
> >> > message
> >> > > in case.dayfile. I am giving those messages below. So far e.c. &
> >> > c.c
> >> > > were achieved up to 2.239... & 5.4599 respectively and already 36
> >> > > iterations are over. My questions are:
> >> > >
> >> > > (1) Is it ok to set up a mixing parameter of 0.15 that is with
> >> > it, is
> >> > > it possible to reach convergence?
> >> > >
> >> > > (2) As plain GGA takes around 80 iterations to converge, is it
> >> > that
> >> > > MBJ potential will take much higher than that as we know it is
> >> > always
> >> > > hard to get convergence with this method?
> >> > >
> >> > > (3) what are the meanings of the given messages below:
> >> > >
> >> > > lapw2 -c -up -vresp (17:12:13) > lapw1 -c -dn (16:19:33)
> >> > > 10848.369u 98.026s 52:39.78 346.4%0+0k 0+1099920io 0pf+0w
> >> > > > lapw1 -c -up (15:26:49) 10864.462u 99.082s 52:44.39
> >> > 346.4%0+0k
> >> > > 0+1100232io 0pf+0w
> >> > > 460.324u 151.313s 6:52.62 148.2%0+0k 0+732368io 0pf+0w
> >> > > -5.956509016536202E-002
> >> > > 3.325214690385789E-002 -9.166205529297161E-002 tauwrong=
> >> > > int:rho,tauw,grho,g2rho 2.146196813781874E-002
> >> > 1.287982148952303E-002
> >> > > -4.564940741427861E-002
> >> > > 3.061850458947012E-002 -5.357427363703868E-002 tauwrong=
> >> > > int:rho,tauw,grho,g2rho 1.778719641126464E-002
> >> > > 1.317651193616000E-002 *what is tauwrong?*
> >> > > -4.561631481999567E-002
> >> > > 3.051935798833875E-002 -5.372842413400847E-002 tauwrong=
> >> > > int:rho,tauw,grho,g2rho 1.783702549056333E-002
> >> > 1.305474408433668E-002
> >> > > -2.872847342414767E-002
> >> > > 2.625149916992486E-002 -2.271097056901070E-002 tauwrong=
> >> > > int:rho,tauw,grho,g2rho 1.456340274765583E-002
> >> > 1.183001700580401E-002
> >> > > -2.843529510619935E-002
> >> > > 2.607602777746414E-002 -2.279192386903682E-002 tauwrong=
> >> > > int:rho,tauw,grho,g2rho 1.462794826548238E-002
> >> > 1.162089194449066E-002
> >> > > -1.211083415464120E-002
> >> > > ..........................................
> >> > > ..........................................
> >> > > > lapw0 (15:19:56) sphere:rho,tauw,grho,g2rho
> >> > 7.46875999972237
> >> > > 180.956718336004
> >> > > > lapw0 -grr (15:15:10) 315.375u 93.253s 4:45.73 143.0%0+0k
> >> > > 0+................
> >> > >
> >> > >
> >> > > Any response in this regard will be very helpful for us. Thanks in
> >> > > advance.
> >> > >
> >> > > with regards,
> >> > > --
> >> > > Shamik Chakrabarti
> >> > > Senior Research Fellow
> >> > > Dept. of Physics & Meteorology
> >> > > Material Processing & Solid State Ionics Lab
> >> > > IIT Kharagpur
> >> > > Kharagpur 721302
> >> > > INDIA
> >> > >
> >> > >
> >> > >
> >> > > --
> >> > > Shamik Chakrabarti
> >> > > Senior Research Fellow
> >> > > Dept. of Physics & Meteorology
> >> > > Material Processing & Solid State Ionics Lab
> >> > > IIT Kharagpur
> >> > > Kharagpur 721302
> >> > > INDIA
> >> > >
> >> > >
> >> > > _______________________________________________
> >> > > Wien mailing list
> >> > > Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
> >> > <mailto:Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>>
> >> > > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >> >
> >> > --
> >> > Dr. pascal Boulet, computational chemist
> >> > University of Aix-Marseille I
> >> > Laboratoire Chimie Provence, UMR 6264
> >> > Group of Theoretical Chemistry
> >> > Avenue Normandie-Niemen
> >> > 13397 Marseille Cedex 20
> >> > France
> >> > **********
> >> > Tel. (+33) (0)413.55.18.10
> >> > Fax. (+33) (0)413.55.18.50
> >> > **********
> >> > http://www.lc-provence.fr
> >> > https://sites.google.com/a/univ-provence.fr/pb-comput-chem
> >> > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >> >
> >> > * Français - détecté
> >> > * Anglais
> >> > * Français
> >> >
> >> > * Anglais
> >> > * Français
> >> >
> >> > <javascript:void(0);>
> >> > _______________________________________________
> >> > Wien mailing list
> >> > Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
> >> > <mailto:Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>>
> >> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >> >
> >> >
> >> >
> >> >
> >> > --
> >> > Shamik Chakrabarti
> >> > Senior Research Fellow
> >> > Dept. of Physics & Meteorology
> >> > Material Processing & Solid State Ionics Lab
> >> > IIT Kharagpur
> >> > Kharagpur 721302
> >> > INDIA
> >> >
> >> >
> >> > _______________________________________________
> >> > Wien mailing list
> >> > Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
> >> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >>
> >> --
> >> Dr. pascal Boulet, computational chemist
> >> University of Aix-Marseille I
> >> Laboratoire Chimie Provence, UMR 6264
> >> Group of Theoretical Chemistry
> >> Avenue Normandie-Niemen
> >> 13397 Marseille Cedex 20
> >> France
> >> **********
> >> Tel. (+33) (0)413.55.18.10
> >> Fax. (+33) (0)413.55.18.50
> >> **********
> >> http://www.lc-provence.fr
> >> https://sites.google.com/a/univ-provence.fr/pb-comput-chem
> >> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> >>
> >> _______________________________________________
> >> Wien mailing list
> >> Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
> >> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >
> >
> >
> >
> > --
> > Shamik Chakrabarti
> > Senior Research Fellow
> > Dept. of Physics & Meteorology
> > Material Processing & Solid State Ionics Lab
> > IIT Kharagpur
> > Kharagpur 721302
> > INDIA
> >
> > _______________________________________________
> > Wien mailing list
> > Wien at zeus.theochem.tuwien.ac.at <mailto:Wien at zeus.theochem.tuwien.ac.at>
> > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> >
>
>
>
> --
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu <http://www.numis.northwestern.edu> 1-847-491-3996
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought"
> Albert Szent-Gyorgi
> _______________________________________________
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>
>
>
>
> --
> Shamik Chakrabarti
> Senior Research Fellow
> Dept. of Physics & Meteorology
> Material Processing & Solid State Ionics Lab
> IIT Kharagpur
> Kharagpur 721302
> INDIA
>
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
--
P.Blaha
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